Common Stock and Warrants - Schedule of Common Stock Reserved for Issuance (Detail) - shares	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Sep. 30, 2021
Class Of Stock [Line Items]
Redeemable convertible preferred stock	209,181,855	0
Outstanding stock options	67,377,463	64,701,181
Shares available for future issuance under equity incentive plan	278,819,076	160,311,865
2006 Equity Incentive Plan
Class Of Stock [Line Items]
Shares available for future issuance under equity incentive plan	2,259,758	0
2021 Equity Incentive Plan
Class Of Stock [Line Items]
Shares available for future issuance under equity incentive plan	0	67,033,576
Private Placement Warrants
Class Of Stock [Line Items]
Class of warrant or right outstanding reserved for future issuance	0	8,113,999
Public Warrants
Class Of Stock [Line Items]
Class of warrant or right outstanding reserved for future issuance	0	16,951,609
Restricted Stock Units [Member]
Class Of Stock [Line Items]
Outstanding restricted stock units	0	3,511,500